Recently, there has been a trend in which the size of a data sector, which is used to record data on magnetic disks, has increased. Such a data sector is called a long sector. The use of the long sector enhances, for example, the efficiency of formatting.
In general, in magnetic disk apparatuses, the data sector is located so as to fall within one track. Therefore, it is assumed that the data sector is located within one track even though the data sector (i.e., long sector) has a large size. When data sectors are located in such manner, it is possible that an area with no data sector (hereinafter referred to as “an extra area”) will occur at, for example, an end portion of a track. It is also possible that the extra area will increase in accordance with an increase in data sector size. In this case, the storage capacity per track decreases.